This invention relates to materials for electrodes in ICs, and specifically to electrode materials having improved hydrogen degradation resistance properties.
Platinum (Pt) has been widely used for top and bottom electrodes in ferroelectric-based capacitors and devices. High temperature hydrogen annealing may be performed to test the integrity and properties of the ferroelectric stack. The major drawback when using Pt as a top electrode is its catalytic nature in the presence of hydrogen. It has been found that the integrity of a Pt top electrode may be severely damaged during 400xc2x0 C. forming gas annealing in just 30 sec. Fujisaki et al., Degradation-free ferroelectric (Pb(Zr, Ti)O3 thin film capacitors with IrO2 top electrode, Integrated Ferroelectrics, Vol. 21, pp. 83-85 (1998). Furthermore, Pt accelerates the decomposition of H2 molecules into atomic hydrogen which will attack and deoxidize the oxide based ferroelectric material, thus degrading their ferroelectric properties.
Titanium oxide (TiO2) has been shown to have passivation properties during hydrogen ambient annealing. A very thin layer of Al2O3 is also effective to protect ferroelectric capacitors, however, use of either TiO2 or Al2O3 requires an additional deposition step, preferably by CVD, to achieve good step coverage.
An electrode for use in a ferroelectric device includes a bottom electrode; a ferroelectric layer; and a top electrode formed on the ferroelectric layer and formed of a combination of metals, including a first metal take from the group of metals consisting of platinum and iridium, and a second metal taken from the group of metals consisting of aluminum and titanium; wherein the top electrode acts as a passivation layer.
A method of forming a hydrogen-resistant electrode in a ferroelectric device includes forming a bottom electrode; forming a ferroelectric layer on the bottom electrode; depositing a top electrode on the ferroelectric layer; including depositing, simultaneously, a first metal taken from the group of metals consisting of platinum and iridium; and a second metal taken from the group of metals consisting of aluminum and titanium; and forming a passivation layer by annealing the structure in an oxygen atmosphere to form an oxide passivation layer on the top electrode.
An object of the invention is to provide an electrode material which may be used in nonvolatile memory devices, DRAMs, capacitors, pyroelectric infrared sensors, optical displays, optical switches, piezoelectric transducers, and surface acoustic wave devices.
A further object of the invention is to provide an electrode material that has improved hydrogen degradation resistance.
Another object of the invention is to provide an electrode material which can maintain integrity and the ferroelectric properties can retained when the ferroelectric capacitor or devices experience a typical hydrogen ambient annealing, at temperatures in a range of about 300xc2x0 C. to 500xc2x0 C.
This summary and objectives of the invention are provided to enable quick comprehension of the nature of the invention. A more thorough understanding of the invention may be obtained by reference to the following detailed description of the preferred embodiment of the invention in connection with the drawings.